Dielectric barrier discharge light sources have been used to produce VUV, UV, visible and IR light for a great variety of purposes. For example, UV light from dielectric barrier discharge light sources has been used for photo-enhanced material deposition, photocuring of paint or lacquers, photocuring of polymers, photo-oxidation of solids, fluids or gases, or sterilization and ultraviolet oxidation of sewage, technical processing water, and drinking water.
Most dielectric barrier discharge light sources or plasma gas light sources have the plasma gas or gas from which the excimers are produced enclosed in a transparent vessel. The transparent vessel is usually glass or quartz, the purity and quality of which can vary considerably. In common arrangements, an electrode is separated by a dielectric barrier from plasma gases enclosed within a container or envelope of dielectric barrier material from a second electrode on the outer surface of the dielectric barrier containing the plasma gases. In some arrangements the electrical discharge light source is simply submersed in fluids to be treated; in other arrangements fluids to be treated with UV light have been circulated through an anulus surrounded by a dielectric barrier and an electrode.
Many light sources emitting in the VUV, UV, visible, and near IR spectral range contain halogens in the gas filling. In most cases halogens are added because the halogens either provide the desired wavelengths by molecular or atomic transitions of the halogen itself, or because the halogens provide precursers for the formation of certain species with another component of the remaining gas filling (e.g., excimers). In the latter case, the desired wavelength or wavelengths are then emitted by the energetical de-excitation of the halogen containing complex.
Because of the high chemical reactivity of halogens, in particular when the halogens are atomized in the gas discharge, the halogens interact with or adsorb onto the glass or quartz plasma gas container. This can reduce the light output, the light efficiency, and the lifetime of the light source because of loss of the halogens to chemical interactions with the container material. Also, the spectral transparency of the glass or quartz container may decrease because of changes in the chemical structure of the glass or quartz container.
Some dielectric barrier discharge light sources have been improved by varying the electrode configurations and materials used for electrodes in combination with use of relatively high gas pressures of halogens. However, the lifetime of halogen-containing dielectric barrier discharge light sources improved in this manner is relatively short at high electrical power of greater than about 1 Watt per cm.sup.2 (generally less than 10 hours) at least partly because of changes in the gases contained within the quartz tubes of the UV lamp.
Because of the often expensive, labor intensive, complicated nature of the task and interruptions of operations associated with change out of no longer functioning dielectric barrier discharge light sources, it is important that the dielectric barrier discharge light sources have as long a lifetime as possible.
Therefore there is a need for ways of increasing lifetimes of any dielectric barrier discharge light source which uses halogens in the plasma gas, and in particular for ways of increasing lifetimes of dielectric barrier discharge light sources which use high gas pressures of halogens.
It is an object of this invention to provide a method of lengthening the lifetime of dielectric barrier discharge light sources which can also be employed in other halogen-containing light sources.
It is also an object of this invention to provide a method of reducing loss of halogen gases from plasma gas mixes used in dielectric barrier discharge light sources and other halogen-containing light sources.
It is another object of this invention to provide dielectric barrier discharge light sources and other halogen-containing light sources with improved lifetimes.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. The claims appended hereto are intended to cover all changes and modifications within the spirit and scope thereof.